I think this has been covered in the distant past, but I have forgotten the answers. It's going back a while.

I have an early Furuno FA50 AIS, connected to MFD8, radar and Maxsea TZ.I'd like to update the AIS, which these days will have NMEA183 and N2k outputs.

As I understand it, I will need to run fast NMEA183 from the AIS to the MFD8. No problem.

So, questions -

Will the MFD8 then output the AIS across the ethernet to TZ?

If AIS arrives at the MFD8 via N2k, is it output on the ethernet also?

The Furuno equipment has given very good service for over seven years now. I have been very pleased with it. I'd update the plotter (I don't need to, it works very well) but Furuno seem to be neglecting the smaller formats. I don't have space for the TZT2.

Yes. AIS will travel over the network from the MFD8 to the TZT. Mixed NN3D/TZT systems should ensure that any NMEA 2000 is connected only to NN3D. TZT should have no NMEA 2000 connections/cables connected when part of the NN3D network.

If AIS arrives at the MFD8 via N2k, is it output on the ethernet also?

No, AIS is not supported from NMEA 2000 with the NN3D.

The Furuno equipment has given very good service for over seven years now. I have been very pleased with it. I'd update the plotter (I don't need to, it works very well) but Furuno seem to be neglecting the smaller formats. I don't have space for the TZT2.

Furuno does offer the TZT9 but I agree that the NavNet systems it would be nice to have a smaller size. The TZT9 is about the size as the old 7" NavNet, I guess that was their line of thinking. We do offer smaller units but not with the NavNet series. It is possible to use the TZTBB and select any size display you want to connect. I am glad to hear you have enjoyed your system.